At the place where I worked, I concocted a scheme for a multi-stage continuous flow system for bleach-fix; as you feed used blix in one end, desilvered blix comes out the other end. The only operator intervention needed was about 20 minutes per day to knock off the silver. (You can probably appreciate what it takes to get 50 lb of silver per day out of several thousand gallons of blix, which we did for a couple peak weeks every year.)
We tried several "silver controllers" way back (probably 1980s?), and were never very satisfied. They had to be somehow calibrated with the user's specific fixer, or perhaps used same as the filling solution in a reference cell. At any rate, we found manual operation more reliable, using operator judgement.To really investigate the plating rate of process you need to look at a number of variables: silver concentration, pH, cathode surface and area, and agitation and you need to monitor the process by measuring the cathode potential with a reference electrode and high input impedance electrometer.
I wish I'd had a better understanding of things back in those days, but I didn't have either the discipline or the interest to learn the fundamentals.